A. E. MURNEEK 333 



Gametogenesis and Fertilization 



Several years ago in work on problems of the relation of nutrition 

 to reproduction of the tomato, it was found that as a result of fertilization 

 (gametic union) and formation of zygotes not only tissues accessory 

 to the embryo and structures immediately subtending the flower (42,35) 

 are stimulated in development, but that metabohsm throughout the plant 

 is accelerated to some extent. This was evidenced by increased absorption 

 of soil nutrients, and assimilation of carbon dioxide (51). It has been 

 confirmed with several other plants (56,94,19,4). 



Subsequently two phases of the observed stimulation during the 

 general period of flowering and fruit setting were recognized, one 

 occurring about the time of synapsis and the other, a more important 

 one, during syngamy (54,55,52,57). Stimulation at synapsis, postulated 

 from general observation and gross analyses of the effects, was later 

 fully established by a former student and colleague of mine (95). It 

 appears to be initiated within the partly developed flower buds con- 

 comitant with chromosome conjugation in the micro- and macrospore 

 mother cells. In the staminate corn flowers the stimulation reaches a 

 peak about 7-12 days after synapsis. The second stimulation, originating 

 from gametic union in the embryo sac, about the time of fertilization, 

 attained a maximal effect in corn some 15 days after pollination (95). 



Undoubtedly responsibility for the two periodic stimulations of growth 

 associated with sexual reproduction lies with a hormone or hormones. 

 Evidence, though not fully conclusive, indicates that it is not due to an 

 increased production of the already well-known heteroauxin. From 100 

 kilograms of 15-day old corn kernels furnished by us, Haagen-Smit et al. 

 (34) extracted all the free Athena- testable hormone, of which only 9 per 

 cent was 3-indoleacetic acid. What is the rest? Contrary to the effects 

 of indoleacetic acid, the crude extracts of immature corn kernels, 

 applied in lanolin paste, were highly active in the production of partheno- 

 carpic tomatoes and peppers. Moreover, Stanley McLane, working in 

 our laboratory, found that in the culture of excised immature corn em- 

 bryos (10-20 days after polhnation) the addition of 3-indoleacetic acid, 

 comparable in concentration to that found in extracts from 15-day old 

 corn, inhibited growth, while a water extract of corn, without the natural 

 indoleacetic acid removed, doubled growth of embryos. 



Shall we call these unknown hormones synapsin and syngamin re- 



